Polymeric supports which have been modified to include an azlactone moiety may be useful for a number of applications. The capability of the azlactone moiety to covalently bind a variety of biologically significant or useful materials to a polymer have allowed the use of azlactone-modified polymers as complexing agents, enzymes, catalysts, polymeric reagents, and chromatographic supports as well as other types of activated supports.
Methods to make azlactone-modified polymers are known. For example, EP 0 392 735 published Oct. 17, 1990 reports suitable methods for attaching an azlactone moiety to a polymer, preferably a polymeric support such as a bead or membrane. The reported processes to produce azlactone modified polymers or polymeric supports include mixing a suitable alkenyl azlactone monomer with a polymer-producing monomer and copolymerizing the mixture of monomers under conditions which do not compromise the reactive properties of the azlactone portion of the resulting copolymer.
Another reported method of attaching an azlactone moiety to a polymeric support involves coating the surface of a polymerized substrate with an azlactone reagent. Reported processes provide a polymer having an azlactone moiety being covalently attached or bound to outer surfaces of the polymeric support. The covalent attachment of the azlactone moiety to the polymer avoids problems typically associated with surface coatings which are not bound to the polymer surface such as leaching of the coating from the polymer surface during the use of the coated polymer.
Another process for attaching an azlactone moiety to a polymeric support is reported in EP 0 392 783 published Oct. 17, 1990. In this report, a monomeric 2-alkenyl azlactone moiety was extrusion grafted to a polyolefin base polymer. The process to prepare such a graft copolymer involved contacting a polyolefin base polymer with a free radical initiator system to give an activated polymer and then reacting the activated polymer with a monomeric alkenyl azlactone moiety. The graft copolymer prepared by the above process provided a polymeric support that had modified surfaces when compared to the base polymer and which retained the desired physical and chemical properties of the azlactone moiety. The reported azlactone graft copolymer may be extruded, formed or molded into a variety of configurations such as beads, pellets, strips, films, or wells and may be used in diverse applications such as thermoplastic adhesives and tie layers for barrier films. In addition, the azlactone moiety may be reacted with nucleophilic reagents such as proteins and other biologically active reagents. The covalent attachment of biological reagents to the polymeric support through the grafted azlactone moiety allows use of the graft copolymers in separation and chromatographic applications.
Microporous films or membranes are one specialized type of material which has potential application in a number of separation or chromatographic uses such as analysis of air, microbiological products, intravenous fluids or vaccines. A specific type of microporous film or membrane is reported in U.S. Pat. No. 4,539,256 to Shipman. This patent reports a microporous film or sheet material that has a microporous structure characterized by having a multiplicity of spaced, randomly dispersed, equiaxed, non-uniformly shaped particles of polymeric material that are connected to each other by a plurality of three-dimensionally dispersed polymeric fibrils.
A method of making this type of microporous film is also reported in U.S. Pat. No. 4,539,256. Briefly, the method of making such a microporous film involves melt blending a crystallizable thermoplastic polymer with a compound which is miscible with the polymer at the melting temperature of the polymer but that phase separates at a temperature at or below the crystallization temperature of the polymer. After the formation of the melt-blend, it is shaped into an article and the article is then cooled to a temperature at which the polymer crystallizes and causes phase separation to occur between the polymer and the compound to give a two phase article. The compound used to form the melt-blend is extracted or removed from the shaped article. Finally, the article is then oriented or stretched in a least one direction to give a network of particles interconnected with fibrils throughout the article.
Although the reported process of Shipman provides a specialized microporous structure, the process requires that the polymer used must be at least partially crystallizable and must be capable of phase separating from a readily removed compound which is used to form the requisite melt-blend. Thus, not all polymeric materials may be used with the reported process to prepare membranes. Importantly, factors or processes expected to destroy or markedly effect the crystallinity of a polymeric material would not be expected to provide suitable polymeric materials for use in the process reported by Shipman.